1. Field of the Invention
The present invention relates to a portable timepiece having a structure of holding a crown such that the crown is not unpreparedly rotated.
2. Description of the Prior Art
There is a portable timepiece adopting a structure of locking a crown by utilizing mesh of screws such that the crown is not unpreparedly rotated in carrying the portable timepiece.
The crown locking structure is a structure in which a winding stem pipe is attached to a case body including a timepiece movement and a female screw portion of a main portion of the crown fitted to a case body outside projected portion is screwed to a male screw portion formed at an outer periphery of the case body outside projected portion of the pipe. Thereby, normally, the crown can be locked by screwing the main portion of the crown to the outer periphery of the case body outside projected portion. Further, in operating the timepiece movement, a winding stem arranged on an inner side of the winding stem pipe can be operated to rotate in a state of pulling to move the crown after disengaging the main portion of the crown from being screwed to the male screw portion (refer to, for example, Patent References 1, 2).
<Patent Reference 1> Japanese Utility Model Application No. 2-57175 (JP-UM-A-4-16394)
<Patent Reference 2> Japanese Utility Model Application No. 5-61093 (JP-UM-A-7-26792)
According to the portable timepiece having the crown locking structure utilizing the mesh of screws, when the crown is left without operating to rotate the crown for a long period of time, there is a case in which an abnormally large force is needed in releasing the crown from being locked by corroding the male screw portion and the female screw portion, or bringing about a biting phenomenon. Further, there is a case in which in accordance with operating to rotate the crown repeatedly, the female screw portion of the crown and the male screw portion of the winding stem pipe brought in mesh with each other are worn or ground. Thereby, a function of locking the crown is deteriorated.